A Multimetal Surface Micromachining Process for Tunable RF MEMS Passives

This paper reports on a microfabrication technology for implementing high-performance passive components suitable for advanced RF front-ends. This technology offers three metal layers with different thicknesses, one dielectric, and two sacrificial layers, enabling the fabrication of continuously tuned capacitors, capacitive and ohmic switches, as well as high-Q inductors all on a single chip. To demonstrate the versatility of this technology, several passive components are fabricated on a Borosilicate glass substrate (epsilon(r) = 4.6). A high-Q tunable capacitor is fabricated exhibiting an electrostatic tuning range of more than 6 : 1. The temperature variation of capacitance from 223 to 333 K is less than 9%, and the tuning speed is better than 80 mu s. To achieve a higher zero-bias capacitance, a tunable capacitor bank is also implemented, which can be tuned from 2.2 pF to 6.1 pF. In addition, a coupled inductor pair with self-inductances of 15 and 21 nH is implemented showing Qs exceeding 40 at 800 MHz. Measurements are compared with high frequency structure simulator (HFSS) electromagnetic simulations, showing good agreement. The technology reported is post-CMOS compatible and low cost.